A gas turbine engine generally includes an engine structure mounting a shaft on oil lubricated bearings housed in a bearing gallery for rotation about an engine axis. The bearing lubrication circuit includes the bearing gallery sealed with running seals to the shaft, a lubricating oil supply line fixed to the bearing gallery and an oil scavenge line.
The oil supply line is in flow communication with an annular oil supply plenum in the bearing gallery; and the lubricating oil scavenge line is in flow communication with a bearing oil bath chamber in the bearing gallery. Oil pump, oil filter, oil heat exchanger and pressure regulator complete the bearing lubrication circuit. During operation of the gas turbine engine, the shaft mounted on the bearing rotates at extremely high speed and generates substantial heat energy in the immediate area of the bearings. To lubricate the bearings and prevent overheating, lubricating oil is pumped from outside the engine core through an oil supply line to the bearing gallery. Oil under pressure is supplied to an annular oil supply plenum in the bearing gallery. The oil supply plenum includes several oil injection openings or nozzles that spray relatively cool oil on the bearings in selected areas. The oil is then collected in an oil bath chamber and may be further circulated or splashed within the bearing gallery and oil bath chamber with oil scoops which splash oil over heated surfaces. The oil bath chamber is evacuated with an oil scavenge line that returns the heated oil to the oil pump, filter and heat exchanger for re-circulation.
Typically the oil is fed from the supply line at approximately 225.degree. F. maximum and after circulating within the bearing area is scavenged at a temperature of approximately 355.degree. F. maximum. The bearings and bearing chamber operate at approximately 375.degree. F. maximum. The bearing gallery includes an air-filled cooling jacket supplied with cool compressed air from the compression section of the engine.
When the gas turbine engine is cool, the bearings may have a temperature equal to the ambient air temperature, for example, as low as -40.degree. F. Therefore, it can be appreciated that the bearings and the bearing gallery experience substantial fluctuations in temperature between non-operating to operating condition.
The oil supply line is fixed into the bearing gallery in a threaded connection to form a rigid oil tight seal and prevent oil leakage into the engine. Due to the expansion and contraction of the inner bearing support ring of bearing gallery, the rigid connection with oil tube can cause significant stress and movement of the bearing gallery. Thermally induced movement of the bearing gallery results in leakage between the rotating shaft and the running seals mounted to the bearing gallery housing.
Therefore, it is desirable to provide a device to connect the oil tube and engine gallery in such a manner as to reduce or eliminate the transmission of thermally induced bearing gallery movement and accompanying stresses to the oil tube while also maintaining the liquid seal to prevent oil leakage into adjacent areas of the engine.